The invention relates to tandem printing and in particular to digital tandem printing systems.
As used herein, the term xe2x80x9cprinting enginexe2x80x9d denotes a device which prints at least a ingle color on a substrate. The term xe2x80x9cprinterxe2x80x9d denotes a device that prints all of the (one or more) color separations for a particular image on a substrate. A printer may include a single printing engine or it may include a number of printing engines. The term xe2x80x9cone-shotxe2x80x9d printer denotes a printer that forms a plurality of color separations on a surface and transfers all of the color separations to the substrate at the same time. xe2x80x9cTandem printersxe2x80x9d are printers that have a series of printers or printing engines through which the substrate passes sequentially for printing.
In general, two types of tandem systems are used. A first such system prints each successive color separation of a color image sequentially, utilizing separate printing engines, for each color. In many such systems the separate stations are in separate units. A second type of tandem system is a xe2x80x9cduplexxe2x80x9d printing system in which one printer is used to print one side of a substrate and a second printer is used to print the other side of the substrate. The first and second printing stations may contain single engines or may have multiple stations for printing multiple separations sequentially. Many tandem printing systems utilize webs as the substrate. In some systems, a plurality of engines print the separations for an image on one side of the substrate and another plurality of engines that print on the other side.
The term xe2x80x9cdigital printerxe2x80x9d is used for a printer in which the image content can be changed between image printings. In particular, the term includes electrostatographic printers such as liquid toner and powder toner electrostatic and electrophotographic printers, ink-jet printers and other printers that electronically determine the printed image.
PCT application PCT/IL98/00553, which is incorporated herein by reference, describes a one-shot digital printing station in which multiple separations are sequentially formed and transferred to an intermediate transfer member and then, transferred from the transfer member to a substrate. One shot printing stations are very suitable for tandem printing and for web printing.
An aspect of some preferred embodiments of the invention is concerned with printing of series of patterns of images along the length of a web.
In a preferred embodiment of the invention a plurality of printers engines print on a web that passes through the stations. In a preferred embodiment of the invention, a group of printers each prints a complete image on a same side of the web. In particular, different printers print on sequential portions of the web. In an especially preferred embodiment of the invention two or more one-shot printers are utilized for printing on the same side of the substrate.
Some preferred embodiments of the invention deal with duplex printing. A first printer, or group of printers prints on a first side of the web. A second printer or group of printers print on the reverse side of the web. At least one of the sides is printed by two or more printers
In preferred embodiments of the invention a first one of the printers prints a series of spaced images on one side of the substrate. A second printer prints spaced images interleaved between the images printed by the first printer. In some embodiments more than two printers are used to print on a single side of the substrate and a higher degree of interleaving may be used.
Preferably, images are printed on the second side of the substrate by a further group of tandem printers, which operate in the same manner as the first and second printers described in the previous paragraph.
In some preferred embodiments of the invention, the printed images are all the same size and are all printed on the same repeat. In others, the size of the images and the repeat are different.
In preferred embodiments of the invention, the separate printers are digital printers, although analog printers (with fixed images) may be used in some embodiments of the invention. When digital printers are used, the size and content of the images is easily controlled and series of images can be printed. In some embodiments all the images printed may be different and/or may have a different size.
There is thus provided, in accordance with a preferred embodiment of the invention, printing apparatus comprising:
a first printer that prints first images at spaced positions, separated by spaces, along a first side of a web; and
a second printer that prints second images at spaced positions within the spaces between the first images.
In a preferred embodiment of the invention, in which spaces remain after printing said first and second images, the apparatus includes a third printer that prints third images at spaced positions within the remaining spaces.
Preferably the apparatus includes at least one reverse side printer that prints images on the other side of the web. In a preferred embodiment of the invention the at least one reverse side printer comprises:
a first reverse side printer that prints images at spaced positions, separated by spaces, along the reverse side of the web; and
a second reverse side printer that prints images at spaced positions within the spaces between the images printed by the first reverse side printer.
In a preferred embodiment of the invention in which spaces remain after printing by said first and second reverse side printers, the at least one reverse side printer comprises a third reverse side print that prints images at spaced positions within the remaining spaces.
Preferably, the images printed by the at least one reverse side printer are aligned with respective ones of the images printed on the first side of the web.
In a preferred embodiment of the invention, the images printed by the first and second printers have different dimensions along the length direction of the web. In preferred embodiment of the invention, different images printed by at least one of the first and second printers have different dimensions in the led direction of the web. In a preferred embodiment of the invention, at least some of the images printed by at least one of the printers are different from e other. In a preferred embodiment of the invention, at least some of the images produced by different printers are different.
In a preferred embodiment of the invention, the images printed by at least some of the printers are multi-color images comprised of a plurality of single color separations. Preferably, each of the separations is sequentially produced and the apparatus includes an intermediate transfer member that sequentially receives the separations and transfers them together to the web.
Preferably, the printers are electrostatographic printers, preferably utilizing either powder or liquid toner.
In a preferred embodiment of the invention, the first and second printers are identical in structure.
In a preferred embodiment of the invention, at least one of the first and second printers is physically the same as one of the fast and second reverse side printers.
There is further provided, in accordance with a preferred embodiment of the invention, a method of printing utilizing a plurality of printers, each capable of printing an image on a same side of a web, the method comprising:
printing, by a first printer, of first images, separated by spaces, along a first side of a web; and
printing, by a second printer, of second images at spaced positions within the spaces between the first images.
In a preferred embodiment of the invention, in which spaces remain after printing said first and second images, the method includes:
printing, by a third printer, of third images at spaced positions within the remaining spaces.
Preferably, the method includes printing at least one image on the other side of the web.
In a preferred embodiment of the invention printing at least one image on the other side of the web comprises:
printing images, by a first reverse side printer, separated by spaces, along the reverse side of the web; and
printing images, by a second reverse side printer, at spaced positions within the spaces between the images printed by the first reverse side printer.
Preferably, where spaces remain after printing by said first and second reverse side printers, the method comprises printing, by a third reverse side printer, of images at spaced positions within the remaining spaces.
Preferably, the images printed on the reverse side are aligned with respective ones of the images printed on the first side of the web. In a preferred embodiment of the invention, the images printed by the first and second printers have different dimensions along the length direction of the web. In a preferred embodiment of the invention different images printed by at least one of the first and second printers have different dimensions in the length direction of the web. In a preferred embodiment of the invention, at least some of the images printed by at least one of the printers are different from each other. In a preferred embodiment of the invention, at least some of the images produced by different printers are different.
In a preferred embodiment of the invention, the images printed by at least some of the printers are multi-color images comprised of a plurality of single color separations. Preferably, each of the separations is sequentially produced and the method includes
sequentially transferring the images to an intermediate transfer member; and
transferring the images together to the web.
Preferably printing comprises printing using electrostatographic printers, preferably using powder or liquid toner.